I have both the VT bass and the Valvedrive on my board. The Valvedrive is my always-on pedal. I keep it at a low gain, just before audible breakup, and it makes my whole signal sound warmer, bigger and thicker with a bit of compression, but doesn't lose any of the character of the signal. You almost can't hear the effect, but it really makes it shine in the mix. I know the glowing tube is a gimmick, but I really like the sound of it.
The VT bass is more versatile, but I almost never turn it on because no matter what anyone says, I feel it scoops the sound in that Ampeg way and is not as warm as the EBS. The EBS makes the mids pop out a bit, while the VT in most settings tends to emphasize the sublows and the extreme highs.
So I much prefer the Valvedrive (for live performance). But that's just me, and I'm not an Ampeg guy. For recording I will probably use the VT bass, as it's quite versatile. You need to try them both out to decide for yourself.